Alright, I'm sick of the noise from my WD2500JS. I need suggestions replacing them. I have two of them, both bad. Subjectively speaking, if my NeoHE is at 20 dba or so, the WD sounds a lot louder, 22-23 during idle I would say. It's also a high pitched whine which stands out from ambient. (I also tested my dad's WD3200KS, it's slightly quieter but still too loud for me.)

By a stroke of good luck, I do have a very quiet 8mb cache Maxtor Diamondmax 10 200gb. It's only slightly noticable over my NeoHE during idle although it's vibes and seeks are not great. I plan to put it back in my rig. However....

I need suggestions for a secondary HDD. Criteria: moderate size (120+), not any louder than the Maxtor during idle (20-21 idle dba? Seek noise doesn't bother me "too" much), available in Toronto for a decent price.

I've been looking at a few:
Another Diamondmax 200, a Seagate 7200.9 160gb single platter, a Samsung SP2504C (expensive, $20 more than other 250gbs unless you find me a good price :p), a WD5000KS (I really doubt if the results on SPCR's review can be duplicated.) I'm also open to other suggestions.

*I've looked at Smartdrives, but they're too expensive especially since I can't find them in Canada.

Unlike most competitors, current Samsung drives (P120 & T133) generate more low-frequency rotational noise, while there is very little of the usual high-frequency noise, both rotational and in seek mode. To my ears it's the best compromise in currently available 250-400 GB 3.5" drives. High freqs can be further reduced with acoustic foam or using a 5.25" enclosure. They run cool but vibration can be a problem if you hard-mount a SP2504C in a thin aluminium case.

The WD3200KS & WD5000KS have very low overall dB/A ratings, comparable to the SP2504C, but their idle noise concentrates more on mid and high frequencies; I think this is what you don't like on your current WD2500JS (provided it's not malfunctioning). As you found your dad's WD3200KS still too loud, I'm not sure the SP2504C would be quiet enough; so maybe one 2.5" drive from the SPCR's recommended list, if lower capacity, lower perfs and higher price still match your needs.

I'd recommend a WD2500KS or WD3200KS over the drives listed. My WD2500KS is quieter than my SP2504C. I got my Samsung on "sale" at Newegg. The "good deals" may even be bad lots, so maybe go with a more expensive drive would be a good idea. How about buying a half dozen various drives and selling the loud ones? Good luck!

I have three DM10 200GB SATA1 drives with AAM set to quiet and will be getting a 4th in a couple of months. Very quiet whooshing noise when idle (zero whine), seeks are barely noticeable, and vibration is low (but does benefit from suspension).

I've noticed the 250GB and higher versions vibrate much more though so be wary of larger drives.

Similar experience here. I bought a WD3200KS a couple of weeks ago, then sold the SP2504C/Nidec. The new Caviar SE16 line seems to be a solid performer.